Although exposure to sunlight and other sources of ultraviolet ("UV") radiation can cause embrittlement and yellowing of some polymers, this polymer degradation may be inhibited by mixing or coating susceptible polymers with compounds know as UV stabilizers.
Trisaryltriazine compounds are particularly effective UV stabilizers. Triazine UV absorbers are a class of compounds which have at least one 2-hydroxyphenyl substituent on the 2-, 4-, and 6-positions of a 1,3,5-triazine ring. See Formula I. ##STR1##
wherein Ar.sub.1 and Ar.sub.2 are aryl or substituted aryl, and R indicates any type of substitution about the 2-hydroxyphenyl. The Ar.sub.1 and Ar.sub.2 aromatic rings may contain other substituents or can be fused polyaromatics. ##STR2##
A preferred class of trisaryltriazine UVAs are based on 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazines, i.e., compounds where there are two non-phenolic aromatic groups and one phenolic aromatic group derived from resorcinol. See Formula II. Of this class of compounds there are a number of commercial products in which the para-hydroxyl group of the phenolic ring is functionalized and the non-phenolic aromatic rings are either unsubstituted phenyl (e.g., TINUVIN 1577) or m-xylyl (e.g., CYASORB UV-1164, CYASORB UV-1164L, and TINUVIN 400). These 2-(2-hydroxy-4-alkoxyphenyl)-4,6-bisaryl-1,3,5-triazines UV absorbers exhibit high inherent light stability and permanence as compared to other classes of UV absorbers such as benzotriazoles and benzophenones. ##STR3##
These compounds are generally made by alkylating the corresponding 4-hydroxy precursor, viz., 2-(2,4-dihydroxyphen yl)-4,6-bisaryl-1,3,5-triazine with alkylating reagents. For example, CYASORB UV-1164 is made by reacting 2- (2, 4-dihydroxyphenyl)-4,6-bis (2, 4-dimethyphenyl) -1,3,5-triazine with 1-octyl halide in the presence of a base. See Scheme I. For a review of the previously known methods for making triazine UVAs, see the following articles: (1) H. Brunetti and C. E. Luethi, Helvetica Chimica Acta, Vol. 55, 1972, pages 1566-1595; (2) S. Tanimoto and M. Yamagata, Senryo to Yakahin, Vol. 40(12), 1995, pages 325-339.
U.S. Pat. No. 3,268,474 to Hardy, et al. describes the formation of 2,4-dihydroxyphenyl-triazine compounds from the reaction of cyanuric chloride with resorcinol derivatives. Tris-aryl-triazines compounds are prepared from the trimerization of substituted aryl amides or aryl nitrites, or the reaction of a cyanuric halide with dialkylated resorcinol. As an example of the latter, cyanuric chloride is allowed to react with excess 1,3-dimethoxybenzene producing a mixture of 2,4,6-tris(2,4-dimethoxyphenyl)-1,3,5-triazine and 2,4-bis(2-hydroxy-4-methoxyphenyl)-6-(2,4-30 dimethoxyphenyl)-1,3,5-triazine compounds.
British Patent Specification 884,802 discloses a method to produce m-xylene substituted mono- or dichlorotriazines from cyanuric acid, m-xylene, and AlCl.sub.3.
European Patent Application 0779280 discloses a method of making 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-s-triazine from cyanuric chloride, m-xylene, and resorcinol in a one pot process.
U.S. Pat. No. 3,244,708 discloses a method to produce ether substituted aryl triazines from resorcinol substituted triazines wherein a base deprotonates the phenolic proton prior to addition of an alkylhalide.
U.S. Pat. No. 5,726,310 to Orban et al. discloses an one pot method of making 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-s-10 triazine by reacting cyanuric chloride with m-xylene in the presence of a Lewis acid to produce intermediate 2-chloro-4,6-bis(2,4-dimethylphenyl)-s-triazine followed by reaction with resorcinol.
U.S. Pat. Nos. 5,084,570 and 5,106,972 to Burdeska et al. disclose a process for the preparation of 2-(2,4-dihydroxyphenyl)-4,6-diaryl-s-triazines from an intermediate 2-methylthio-4,6-diaryl-s-triazine.
Reaction of cyanuric chloride with phenols formation of either C-alkylation or 0-alkylation has been reported depending on the phenol substituents. Y. Horikoshi et al., NipDon Kaaaku Kaishi, 3, (1974) 530-535; CA 81:152177.
More recently Japanese Patent JP 09-059263 discloses a process to make 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine compounds from reaction of 2-oxyaryl-25 4,6-bisaryl-1,3,5-triazine compounds with resorcinol and AlCl.sub.3.
In light of the above references and difficulties unique to large scale syntheses of triazine compounds, a few preferred methods of making 2-(2-hydroxyl-4-alkoxyphenyl)-30 4,6-bisaryl-1,3,5-triazine compounds have emerged. These methods, which typically culminate in the alkylation of 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine, have several limitations.
One limitation stems from the fact that 2-(2,4-dihyroxyphenyl)-4,6-bisaryl-1,3,5-triazine has very poor solubility requiring either very high dilution or difficult stirring. On the other hand, in the prior art, 2-chloro-4,6-bisaryl-1,3,5-triazines are first reacted with resorcinol to form 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-5 triazines. Such reaction mixtures are difficult to stir as two immiscible layers are formed, and the lower layer containing the aluminum chloride complexes of the product is generally very thick and tarry sticky mass. Moreover, the isolation of the 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazines is not easy due to the poor solubility of such compounds in common organic solvents. An additional drawback is that another step (alkylation step) is needed to make the final product, 2-(2-hydroxy-4-alkoxyphenyl)-4,6-bisaryl-1,3,5-triazines, from 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-15 1,3,5-triazines. The reaction of cyanuric chloride and an aryl compound in the presence of aluminum chloride is typically used to produce 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine.
For some aryl compounds, however, this reaction produces the bisaryl compound in low yield, instead preferring to form either the monoaryl or trisaryl compounds. For example, it has been observed by the inventors that 2-(2-hydroxyl-4-alkoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine is highly reactive under typical reaction conditions, and quickly reacts additional m-xylene, as shown in Scheme II: ##STR4##
wherein Ar is m-xylene.
Under carefully controlled conditions, and from some aryl groups, this reaction can provide sufficient amounts of certain 2-chloro-4,6-bisaryl-1,3,5-triazine compounds. These may then be reacted with resorcinol in another reaction catalyzed by aluminum chloride to form the corresponding 2-chloro-4,6-bis(2,4-dihydroxyphenyl)-1,3,5-triazine compounds, as shown in Scheme III: ##STR5##
Once the desired 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine compound has been formed, it can then be alkylated to yield the final 2-(2-hydroxy-4-alkoxyphenyl)-4,6-bisaryl-1,3,5-triazine product, as shown in Scheme IV: ##STR6##
The commercially available UV stabilizer CYASORB.RTM. UV-1164 has been made this way by reacting 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine with 1-octyl halide in the presence of a base, as shown in Scheme V: ##STR7##
The synthetic process described above can be effective in some cases, yet it has several disadvantages that can render the production of certain UV stabilizers costly and inefficient. For example, this approach is of little use for the production of mixed aryl 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine compounds, since the reaction of cyanuric chloride with a mixture of aryl groups typically forms a mixture of products that are difficult to separate.
As was alluded above, another disadvantage of this process is that the type of aryl group initially reacted with cyanuric chloride can have a dramatic effect on the resulting product mixture. For example, the reaction of xylene and cyanuric chloride in a 2:1 ratio yields a mixture of made up almost exclusively of mono- and tri- substituted xylene triazine compounds. By contrast, the present inventors have discovered that the major product of the reaction of cyanuric chloride with resorcinol is the bis(resorcinol) compound 2-chloro-4,6-bis(2,4-dihydroxyphenyl-1,3-5-triazine. Consequently, variation of the aryl group can lead to unanticipated extraction, separation, and purification problems. These problems render the formation of mixed aryl triazine compounds especially difficult.
These problems are not solved by the aluminum chloride catalyzed reaction of resorcinol and 2,4-bischloro-6-aryl-1,3,5-triazines, as this reaction typically produces an intractable, undesirable reaction mixture. Two immiscible layers are formed upon initiation of the reaction, the lower of which contains aluminum chloride complexes of the products, and is typically a thick, tarry, sticky mass that renders the reaction mixture very difficult to stir. Furthermore, the poor solubilities of the resulting 2,4-hydroxyphenyl triazine compounds hinders their isolation, and leaves comparatively little material for the third step of the reaction.
The present invention avoids the problems described above in part by employing the catalyzed reaction of aryl ethers and halogenated triazine compounds. Many of these reactions are heretofor uncharacterized. For example, the present inventors could not find in the literature a description of the reaction of 3-alkoxyphenol and a 2,4-dichloro-6-aryl-1,3,5-triazine. It was consequently unclear what such a reaction would yield, as shown in Scheme VI: ##STR8##
That the reaction of an alkoxyphenol and a substitute triazine could form several different products in an unlimited number of ratios is clear from the literature.
It has been reported that the reaction of cyanuric chloride with phenols can yield both C--C and C--O linked products. See, e.g. Y. Horikoshi et al., Nippon Kaqaku Kaishi, 3, (1974) 530-535; CA 81:152177. For example, Japanese Patent 09-059263 describes the formation of C--O linked products from the reaction of cyanuric chloride and substituted pheols, as shown in Scheme VII: ##STR9##
wherein R.sub.1 and R.sub.2 are H, C.sub.1-10 alkyl, alkoxy, alkenyl, halo, or nitro.
In light of these references, and as shown in Scheme V above, until now it was unclear weather the reaction of cyanuric chloride and 3-alkoxyphenol would yield C--C or C--O linked products. Furthermore, the regiochemistry of the preferred products of the reaction was also unknown, as was whether the reaction would allow the selective monosubstitution of chlorotriazine. By studying this reaction, the present inventors have surprisingly found a particularly effective means of synthesizing triazine compounds suitable as UV stabilizers.